Study on the carbon sequestration performance and barrier mechanism of biochar cement-based vertical cutoff walls for phenol pollution in groundwater

In this study, a new barrier material was synthesized using biochar to modify the cement-bentonite (CB) system. The optimal doping of biochar in the CB system was determined to be 20 % through mechanical performance, gas permeability and adsorption efficiency tests. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) results indicated that biochar enhanced the hydration of the cement system and the fixation of carbon dioxide. Adsorption kinetics and isotherm experiments indicated that the adsorption reaction of the material to phenol was more consistent with the pseudo-second-order kinetic model and the Freundlich model. Diffusion tests revealed that the average effective diffusion coefficient of the material at different NaCl concentrations was 8.980x10-12 m2/s. The X-ray tomography and finite element simulation results indicated that the sample had an average pore radius of 15.66 mu m, with poor permeability and low pore connectivity. The study on engineering performance indicated that the service life of the cutoff wall increased with the thickness and the flow resistance coefficient. Service life calculations and Visual MODFLOW simulations showed that the CBB-2 cutoff wall has significant durability and barrier effect to phenol.